Glass building block



FIG. 1 is a front perspective view of a glass building block showing my new design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is an elevational view thereof taken from the bottom of FIG. 5;

FIG. 4 is an elevational view thereof taken from the left of FIG. 5;

FIG. 5 is a top plan view thereof; and

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 2. 

The ornamental design for a glass building block, as shown and described. 